Electromagnet



H. A. MAXFIELD ELECTROMAGNET June 1,1926. 1,587,170

Original Filed March16, 1922 Patented June 1 1926.

' UNITED STATES insane PATENT caries.

I HAROLD A. IVIAXISIELD, 0F WO;RCESTEB, -MASSACI-1USETTS.

ELECTROMAGNET.

Original application filed March 16, 1922, Serial No. 544,259. Divided and this application filed .Tune 22,

1922. Serial My invention relates to electromagnets and its object is to provide electromagnetic, instead of resilient, means tocounterbalance the normal magneticpull of an electromagnet the armature of which is moved fronrits normal position only'when the energizing current-exceeds a given intensity.

While my invention is peculiarly adapted for use in an automatic train control system such as disclosed in my application Serial No. 544,259, filed March 16, 1922, on which Letters Patent 1,485,563 were granted March 4, 1924, or" which this application is a -divi- .sion, it is nevertheless adapted to, various other uses, such for example as a vibrator, an overload circuit breaker, a current regulator, etc.

With the foregoing object in View-my invention comprises an electromagnet having co-acting windings which may be relatively movable, said windings beingwarranged to produce co-operating and opposing fields which are so related that the armature is held a givenposition by the resultant magnetic field due to normal energizatlon, and is attracted to another position when such energization becomes excessive.

The drawings which accompany and form a part of this application show two embodiments of my invention, but it will be understood that various modificationsmay be made both in theapparatusand in the circuits in which such apparatus is used without departing from the invention as defined by the appended claims.

In the drawings,-

Figure 1 is a central vertical section of a magnet embodying my invention;

Fig. 2 is a diagram'illustrating one of various ways in which the magnet shown in Fig. .1 may be employed;

.Fig. .3 is a central vertical section of a modification of the magnet shown in Fig. 1;

Fig. 4 is a diagram illustrating one of various ways in which the magnet shown in Fig. 3 may be employed.

In the particular drawings selected for more fully disclosing my invention 10 is an iron casing enclosingthe serially-connected windings 11 and 12. and formingpart of the magnetic circuit thereof, said windings preferably being separated by theiron disc 13which forms a part of the magnetic circuit of each of saidwindi-ngs. Secured to the brass or non-magnetic plunger rod 14 carrying the switch 15, shown in the present instance as provided with a conducting ring 16 arranged between two insulating rings 1'7, 17 is an iron plunger 18 which is separated from the stationary cores 19, 20 by the thin nonmagnetic spacers 21, 22, a brass sleeve 23 preferably being employed to guide the plunger 18 and protect the windings. The coils 11, 12, are wound in the same sense and the coil 24 which is electrically independent of the other two coils is wound in the opposite sense and has its terminals permanently connected to a source of current, the connections being shown in Fig. 2 as the wires 25, 26 connected to the generator 27. I

In the particular instance illustrated in Fig. 2 which represents one of various ways in which the magnet above described may be employed, the coils 11, 12 are serially connected with each other, the generator 27,

the brushes '28, 28 and the conducting ring 16 of the switch.

The load on the generator is represented conventionally at 29.

Under normal conditions the plunger 1b is held against the core 20 by the energization of the magnet 24. The field set up'by the current Iiow in the winding 12 opposes that developed by the winding 24, but the circuits and coils are so designed that when the generator is normally loaded the field of said winding 12 will be substantiallyequal to one-half ofthat created by the coil 24 so that the resultant field will continue to hold the plunger 18, and consequently the switch 15 attached to the lower end of the plunger rod, positively in lowermost position, and

thereby maintain the external circuit of the generator closed at said switch. The coil 11 is so designed that its field will' not be strong enough to attract the plunger 18 to the upper core 19 under the conditions above men= tioned. However, should the generator become short-circuited or'its load materially increased for any reason, the current in tensity in the coils 11, 12 will be materially increased, for example, doubled, and the field of the coil 12 will then practically neutralize that of the coil 24, so that the magnetic force created by the coil 11 will cause the plunger 18 to rise to its uppermost position against the core 19, thereby opening the circuit of the generator.

windings 31, 32, 33 and 3st and forms part of their magnetic circuits. The cores 35, 36 are fixed and the plunger 37 attached to the brass or non-magnetic rod 38 carries said winding 33, and the iron disc preferably is employed to separate the upper and lower stationary coils and to form a part or the magnetic circuit. A non-magnetic sleeve ll) may be used for guiding the plunger and protecting the windings, and thin non-magnetic spacers ll, 12 may be used to separate the plunger from the stationary cores 35, 36. lhe winding 33 is carried the plung er 37 and arranged in a groove out into the periphery of the same.

As shown in Fig. lthe winding 33 con nected by flexible leads 43, ll to the wiud'ng's 31 and 32 and is wound in the same direction as winding 31 and in the oppo: direction from winding 32. The coil 3 s wound in the same direction as the coils 31, 33 and in the opposite direction from coil 32 and is permanently connected to a source current such as the generator by the conductors 46, 47.

The direction of the windi and the current is such that the fields set up by the coils 31, 33 are in the same direction and thereby tend to att "act the plunger against the upper core The field set up by the wind ing 34 is also in the same direction as that created by the windings 31, 33, and therefore the fields 01" the winding 3% and the winding 33 carried by the plunger will react to hold said plunger against the lower core 36. The .field developed by the winding 32 opposing those of the windings 33 and 34 tends to neutralize the field oi winding 3st and by its reaction on that ol winding 33 to repel the plunger upwardly.

Referring to 4 which aforesaid represents one 01 several ways in which the magnetshown in Fig. 3 may be employed, the external circuit of the generator 115 the load of which is represented conventionally at 18 is normally closed through the b 49 and the conducting ring 50 of the 51 consisting as shown of said ring a aged between two msulating rings 52, and includes the serially-connected coils 32 and 33. Under normal conditions the field dcveloped by the winding 3% 1S stron than that of the coil 32 so that the resulant field being in the same direction as that of the coil 33 carried by the plunger will hold the latter against the lower core 36 notwithstanding the relatively weak influence of the field of the coil 31 which tends to draw said phin'ger against the upper core 35.

If however the load on the generator is unduly increased as by a short-circuit, "he field developed by the coil 32 is strcn gthened and overcomes the field of winding 34L, so that the resultant field, being opposite in direction to that of the coil 33 carried by he plunger, repels said plunger, and the .aiter is also attracted by the strengthened field set up by the increased current in the winding 31, whereby die external circuit of the generator is opened at the switch 51.

It will be apparent that many other arrangements of circuits may be employed whereby the magnets above described may be used to control a circuit connected to a source of electrical energy.

Having thus described illustrative embodiments cl my invention without howc'er limiting the same thereto, what I claim and desire to secure by Letters Patent is 1. An electron'iagnet having two axiallyseparated and electrically-connected coils, said coils being wound and connected to create similarly-directed magnetic fields, a magnetic member interposed between said coils and constituting a part of the mageti.c circuit of each, a third coil located within the field or" one of said two coils and wound and connected to create a magnetic field opposing that of said two coils, and an armature located within the fields developed by all of said coils.

2. [in electromagnet having two axiallyseparated and electrically-connected coils, said coils being wound and connected to create similarly-directed magnetic fields, a magnetic member interposed between said coils and constituting a part of the magnetic circuit of each, a third coil axially separated from one of said coils and concentric with the other, said third coil being wound and connected to create a magnetic field opposing that of said two coils, and an armature located within the fields developed by all of said coils.

3. An electromagnet having two axiallyseparated and electrically-connected coils of relatively low resistance and a comparatively small number of turns, said coils being wound and connected to create similarly-directed magnetic fields, a magnetic member interposed between said coils and constituting a part oi the magnetic circuit of each, a third coil located within the fields of said two coils and having relatively high resistance and a comparatively large number of turns, said third coil being wound and connected to create a magnetic field opposing that of said two coils, and an armature located within the fields developed by all of said coils.

l. An electromagnet hav'ag two axiallyscparated and serially-connected coils, said coils being wound and connected to create similarly-directed magnetic fields, a magnetic member interposed between said coils and constituting a part of the magnetic cirsuit of each, a third coil located within the fields of said two coils and wound and con nected to create a magnetic field opposing that of said two coils, and an armature l0- cated within the fields developed by all of said coils.

5. An electromagnet having two axiallyseparated and electrically-connected coils, said coils being wound and connected to create oppositely-directed magnetic fields, a third coil located within the field of one of said coils, an armature for said electromagnet, and a coil carried by said armature, the armature-carried coil being electrically connected with the two first mentioned coils.

6. An electromagnet having two axiallyseparated and electrically-connected coils, said coils being wound and connected to create oppositely directed magnetic fields, a third coil axially separated from one of said coils and concentric with the other, an

armature for said electromagnet' and a coil carried by said armature, the armature-carried coil being electrically connected with the two first mentioned coils.

7. An electromagnet having two axiallyseparated and electrically-connected coils of relatively low resistance and a comparatively small number of turns, said coils being wound and connected to create oppositely directed magnetic fields, a third coil located within the field of said two coils and having relatively high resistance and a comparatively large number of turns, an armature for said electromagnet and a coil carried by said armature, the armature-carried coil being electrically connected with the two first mentioned coils.

8. An electromagnet having two axiallyseparated coils said coils being wound to create oppositely directed magnetic fields, a

third coil located within the fields of said two coils, an armature for said electromag net and a coil carried by said armature, the

two first mentioned coils and the armaturecarried coil being serially connected.

In testimony whereof, I have hereunto subscribed my name this 20th day ofJune, 1922.

HAROLD A. MAXFIELD. 

